The present invention relates generally to fiber optic cables and, more particularly, to fiber optic cables having a filling compound and/or grease layers that have agglomerates of filler particles having significantly reduced major dimensions.
One common type of fiber optic cable includes one or more buffer tubes with a plurality of optical fibers disposed in each of the buffer tubes. For example, a fiber optic cable having a central buffer tube design includes a single buffer tube and a plurality of optical fibers extending lengthwise through the buffer tube. Alternatively, the fiber optic cable can include a plurality of buffer tubes, typically stranded about a central strength member. In either instance, each buffer tube may be filled with a filling compound. The filling compound primarily serves to prevent water ingress into and water propagation through the buffer tube. Moreover, the filling compound helps to maintain the optical fibers in a state of relatively low stress.
Conventional filling compounds are a grease comprised of a base component and a filler or thickener that adjusts the viscosity of the grease to an appropriate level. The base component can be formed of a variety of oils including hydrocarbon-based oils and polyalphaolefin-based oils or a polyglycol based oil. The filler is typically formed of a plurality of particles of silica, clay or the like and generally comprises no more than about 6% by weight of the filling compound. Additionally, the filling compound can include a polymer or rubber component in order to further thicken the grease, and a bridging agent to increase the yield strength of the grease without correspondingly increasing the viscosity of the grease.
In a typical ribbon cable, a plurality of ribbons of optical fibers extend lengthwise through the buffer tube. Typically, the ribbons are stacked and a helical twist is imparted to the lengthwise extending ribbon stack. In a ribbon cable, the filling compound not only fills the space within the buffer tube that surrounds the ribbon stack, but grease layers may be applied between each pair of adjacent ribbons of optical fibers. Among other things, the grease layers are intended to facilitate slight movement between adjacent ribbons of optical fibers as forces are applied to the ribbons. Typically, the grease layers are formed of the same material as the filling compound and therefore generally include a base component, such as an oil, and a filler that is typically formed of particles of silica, clay or the like.
The filler particles generally form agglomerates, each of which is formed of a plurality of particles. In a typical filling compound such as a Dussek Campbell 5264 filling compound, for example, the filler is formed of a plurality of agglomerates of silica particles. The size of the agglomerates varies, but the majority of the agglomerates have cross-sectional sizes above 100 microns, with some agglomerates having cross-sectional sizes that exceed 300 microns. By way of comparison, a typical optical fiber has a cross-sectional diameter of about 250 microns. Thus, some agglomerates may actually be larger than the optical fiber.
The agglomerates can cause difficulties, both during the fabrication of the fiber optic cable and during the operational life of the fiber optic cable. In some instances, the agglomerates may become lodged in equipment and obstruct the application of the grease. The fabrication process must then be temporarily halted and the equipment must be serviced in order to clear the agglomerates from the port. Additionally, the agglomerates can cause performance issues, e.g., microbending of the optical fibers which, in turn, can cause attenuation of the optical signals transmitted by the optical fibers. In this regard, the optical fibers that are at or near the comers of the ribbon stack are particularly susceptible to microbending as a result of the helical twist of the ribbon stack. The optical signals transmitted by the optical fibers that are at or near the comers of the ribbon stack may accordingly be disadvantageously attenuated.
It is oftentimes desirable to increase the fiber packing density of a fiber optic cable, such as a ribbon cable. As such, fiber optic cables have been designed in which the grease layers between the pairs of adjacent ribbons of optical fibers are reduced in thickness. For example, conventional fiber optic cables may include grease layers between the pairs of adjacent ribbons that have a thickness of between about 60 microns and 200 microns. Since the agglomerates that are larger than the grease layer are capable of causing microbending, fiber optic cables having thinner grease layers may experience increased microbending and correspondingly increased attenuation.
In view of the foregoing, a fiber optic cable according to one aspect of the present invention includes a buffer tube defining a lengthwise extending passageway; a plurality of ribbons of optical fibers extending through the passageway defined by the buffer tube; and a grease layer disposed between at least one pair of adjacent ribbons of optical fibers, wherein the grease layer includes a base component and a plurality of agglomerates formed of silica particles with the majority of the agglomerates having a major dimension of less than about 100 microns. In one embodiment, the fiber optic cable of this aspect of the present invention further includes a filling compound that at least partially fills the passageway defined by the buffer tube and that also includes a base component and a plurality of agglomerates comprised of silica particles.
A fiber optic cable according to another aspect of the present invention includes a buffer tube defining a lengthwise extending passageway; a plurality of ribbons of optical fibers extending through the passageway defined by the buffer tube; and a grease layer disposed between at least one pair of adjacent ribbons of optical fibers that has a thickness of no more than 50 microns and that includes a base component and a filler formed of a plurality of agglomerates, the majority of which have a major dimension of less than about 100 microns. In one exemplary embodiment, each agglomerate is comprised of a plurality of particles of either silica or clay.
According to yet another aspect of the present invention, a fiber optic cable includes a buffer tube defining a lengthwise extending passageway; a plurality of optical fibers extending through the passageway defined by the buffer tube; and a filling compound that is disposed within the buffer tube and surrounds the plurality of optical fibers and that includes a base component and plurality of agglomerates formed of silica particles, wherein a majority of the agglomerates have a major dimension of less than about 100 microns. In one embodiment, the fiber optic cable of this aspect of the present invention also includes a plurality of grease layers disposed between adjacent ribbons of optical fibers. Each grease layer of this embodiment of the fiber optic cable also includes a base component and a plurality of agglomerates with the majority of the agglomerates having a major dimension that is less than 100 microns. For example, the filling compound and the plurality of grease layers of this embodiment may be formed of the same compound.